In:
Journal of Endocrinology, Bioscientifica, Vol. 153, No. 3 ( 1997-06), p. 411-421
Abstract:
TRH-like immunoreactivity (TRH-LI) was estimated in methanolic extracts of rat tissues and blood by RIA using antiserum 4319, which binds most peptides with the structure pGlu-X-ProNH 2 , or antiserum 8880, which is specific for TRH (pGlu-His-ProNH 2 ). TRH-LI (determined with antiserum 4319) and TRH (determined with antiserum 8880) contents were 8 and 8 ng/g in brain, 216 and 222 ng/g in hypothalamus, 6·5 and 6 ng/g in pancreas, 163 and 116 ng/g in male pituitary, 105 and 77 ng/g in female pituitary, 1 and 0·1 ng/g in salivary gland, 61 and 42 ng/g in thyroid, 12 and 3 ng/g in adrenal, 3 and 0·3 ng/g in prostate, and 11 and 0·8 ng/g in ovary respectively. Blood TRH-LI (antiserum 4319) and TRH (antiserum 8880) levels were 31 and 18 pg/ml in male rats, and 23 and 10 pg/ml in female rats respectively. Unextracted serum obtained from blood kept for at least 1 h at room temperature no longer contained authentic TRH but still contained TRH-LI (males 20·3 ± 3·1, females 15·9 ± 3·0 pg/ml; means ± s.e.m. ). Isocratic reverse-phase HPLC showed that TRH-LI in serum is largely pGlu-Glu-ProNH 2 ( 〈 EEP-NH 2 ), a peptide previously found in prostate and anterior pituitary. In urine, TRH-LI (antiserum 4319) and TRH (antiserum 8880) levels were 3·21 ± 0·35 and 0·32 ± 0·04 ng/ml in male rats and 3·75 ± 0·22 and 0·37 ± 0·04 ng/ml in female rats respectively (means ± s.e.m. ). Anion-exchange chromatography on QAE-Sephadex showed that urine of normally fed rats contains both basic/neutral TRH-LI (b/nTRH-LI) and acidic TRH-LI (aTRH-LI) in a ratio of ≈ 40:60, and further analysis by HPLC indicated that aTRH-LI represents 〈 EEP-NH 2 . Analysis of food extracts and urine from fasted rats demonstrated that b/nTRH-LI is derived from food particles spilled by the rats during urine collection, while aTRH-LI is endogenously produced. While urinary aTRH-LI levels were higher in female than in male rats (2·99 ± 0·41 vs 2·04 ± 0·20 ng/ml), the daily urinary excretion was similar in both sexes (females 15·6 ± 1·4, males 19·5 ± 2·0 ng/day). Intravenously injected 〈 EEP-NH 2 disappeared from serum with a half-life of ≈ 1 h, and was recovered unchanged and quantitatively in urine. In contrast, when 〈 EEP-NH 2 was administered with food, only ≈ 0·5% was recovered in urine. The urinary clearance rate of serum TRH-LI amounted to 0·52 ± 0·10 ml/min in males and 0·34 ± 0·05 ml/min in females. In view of the presence of 〈 EEP-NH 2 in the anterior pituitary gland, and the regulation of its content in parallel with gonadotrophins, we examined the possibility that serum 〈 EEP-NH 2 is of pituitary origin and correlates with gonadotrophin secretion. However, treatments that alter pituitary 〈 EEP-NH 2 content and gonadotrophin release had no effect on serum TRH-LI or urinary aTRH-LI. In conclusion, the TRH-like peptide 〈 EEP-NH 2 is present in rat serum and is excreted into the urine. Moreover, 〈 EEP-NH 2 in serum and urine is not derived from rat food and is probably not of pituitary origin. Journal of Endocrinology (1997) 153, 411–421
Type of Medium:
Online Resource
ISSN:
0022-0795
,
1479-6805
DOI:
10.1677/joe.0.1530411
Language:
Unknown
Publisher:
Bioscientifica
Publication Date:
1997
detail.hit.zdb_id:
1474892-7
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